From: Pedro Alves <pedro@palves.net>
To: Tom de Vries <tdevries@suse.de>, gdb-patches@sourceware.org
Cc: Tom Tromey <tom@tromey.com>
Subject: Re: [PATCH][gdbsupport] Use task size in parallel_for_each
Date: Fri, 22 Jul 2022 01:03:43 +0100 [thread overview]
Message-ID: <a624f5a9-72b8-4dc6-7458-f1e705d7b9c0@palves.net> (raw)
In-Reply-To: <75931310-5dcd-059d-9221-6c94dbcd231f@suse.de>
On 2022-07-21 9:23 p.m., Tom de Vries wrote:
> On 7/21/22 19:35, Pedro Alves wrote:
>>> diff --git a/gdbsupport/parallel-for.h b/gdbsupport/parallel-for.h
>>> index bf40f125f0f..3c9269574df 100644
>>> --- a/gdbsupport/parallel-for.h
>>> +++ b/gdbsupport/parallel-for.h
>>> @@ -134,7 +134,9 @@ typename gdb::detail::par_for_accumulator<
>>> typename std::result_of<RangeFunction (RandomIt, RandomIt)>::type
>>> >::result_type
>>> parallel_for_each (unsigned n, RandomIt first, RandomIt last,
>>> - RangeFunction callback)
>>> + RangeFunction callback,
>>> + std::function<unsigned int(RandomIt)> *task_size_ptr
>>> + = (std::function<unsigned int(RandomIt)> *)nullptr)
>>
>> That use of a std::function pointer looks odd. AFAICT, TASK_SIZE_PTR is only ever called
>> as a callback by parallel_for_each, for setup, in the calling thread, and isn't stored
>> anywhere, right? If so, gdb::function_view instead should work, is lightweight, and is
>> nullable, meaning you don't need a pointer.
>>
>> And then, at the caller, just using a lambda instead of a std::function should work too:
>>
>> auto task_size = [=] (iter_type iter)
>> {
>> dwarf2_per_cu_data *per_cu = iter->get ();
>> return per_cu->length ();
>> };
>
> I've tried that (attached) but ran into the usual template error mess, not sure how I could solve that yet.
I see. The problem is that here:
@@ -134,7 +135,9 @@ typename gdb::detail::par_for_accumulator<
typename std::result_of<RangeFunction (RandomIt, RandomIt)>::type
>::result_type
parallel_for_each (unsigned n, RandomIt first, RandomIt last,
- RangeFunction callback)
+ RangeFunction callback,
+ gdb::function_view<unsigned int(RandomIt)> task_size
+ = nullptr)
parallel_for_each is a template, and the function_view parameter's type depends
on a template parameter (RandomIt), so we can't rely on implicit conversions, such
as when passing a lambda (lambda -> function_view). We need to pass a function_view of
the right type already. That's not special about function_view, it's just how templates
and overload resolution works.
So this would fix it:
diff --git c/gdb/dwarf2/read.c w/gdb/dwarf2/read.c
index 23c3873cba6..06df773f1e0 100644
--- c/gdb/dwarf2/read.c
+++ w/gdb/dwarf2/read.c
@@ -7067,11 +7067,12 @@ dwarf2_build_psymtabs_hard (dwarf2_per_objfile *per_objfile)
using iter_type = decltype (per_bfd->all_comp_units.begin ());
- auto task_size = [=] (iter_type iter)
+ auto task_size_ = [=] (iter_type iter)
{
dwarf2_per_cu_data *per_cu = iter->get ();
return per_cu->length ();
};
+ gdb::function_view<unsigned (iter_type)> task_size = task_size_;
Though it's annoying to have to write the function_view type.
Note that this instead, is a bad pattern with function_view (similarly
to other view types, like string_view), as it immediately dangles the lambda
temporary:
- auto task_size = [=] (iter_type iter)
+ gdb::function_view<unsigned (iter_type)> task_size = [=] (iter_type iter)
{
dwarf2_per_cu_data *per_cu = iter->get ();
return per_cu->length ();
};
I think the best is to introduce a gdb::make_function_view function,
so that you can do this:
diff --git c/gdb/dwarf2/read.c w/gdb/dwarf2/read.c
index 23c3873cba6..255b955a54c 100644
--- c/gdb/dwarf2/read.c
+++ w/gdb/dwarf2/read.c
@@ -7101,7 +7101,7 @@ dwarf2_build_psymtabs_hard (dwarf2_per_objfile *per_objfile)
}
}
return result_type (thread_storage.release (), std::move (errors));
- }, task_size);
+ }, gdb::make_function_view (task_size));
/* Only show a given exception a single time. */
std::unordered_set<gdb_exception> seen_exceptions;
I've got that working here. I'll post it tomorrow.
Note: the 'task_size' lambda doesn't actually need to capture anything:
@@ -7067,11 +7067,12 @@ dwarf2_build_psymtabs_hard (dwarf2_per_objfile *per_objfile)
using iter_type = decltype (per_bfd->all_comp_units.begin ());
- auto task_size = [=] (iter_type iter)
+ auto task_size = [] (iter_type iter)
{
dwarf2_per_cu_data *per_cu = iter->get ();
return per_cu->length ();
};
next prev parent reply other threads:[~2022-07-22 0:04 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-18 19:42 Tom de Vries via Gdb-patches
2022-07-21 17:35 ` Pedro Alves
2022-07-21 20:23 ` Tom de Vries via Gdb-patches
2022-07-22 0:03 ` Pedro Alves [this message]
2022-07-22 11:07 ` Pedro Alves
2022-07-22 17:07 ` Tom de Vries via Gdb-patches
2022-07-22 19:08 ` Tom Tromey
2022-07-22 19:38 ` Simon Marchi via Gdb-patches
2022-07-23 3:17 ` Tom Tromey
2022-07-22 21:21 ` Tom Tromey
2022-07-23 6:51 ` Tom de Vries via Gdb-patches
2022-07-31 8:38 ` Tom de Vries via Gdb-patches
2022-07-23 5:55 ` Tom de Vries via Gdb-patches
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